This invention relates to an improvement of a wide-angle optical door viewer being set through a door or the like, by which from inside of the door any person or a material object of the outside is able to be certainly watched in the wide-angle in accordance with preparation of the wide angle vision.
Conventionally, in a house, hotel or office, a door viewer was set to quickly watch, without being noticed by anyone or a visitor come abruptly, for prevention against crimes. However, in view of a substantial construction that the inside diameter of a cylindrical member of the assembled door viewer is limited to a small size about 9.5 mm, it is known that it is difficult to come into sight more than 190 degrees of the field of the outside vision and it is difficult to realize such wide-angle outside vision under a circumstance of requirement of miniaturization of the cylindrical member being assorted each lens therein. Also it was required very complex steps for manufacturing the all parts and assembling thereof. In this field, it is well known that the conventional door viewer is comprised of assembled two objectives and one eyepiece, and that the conventional construction which is put the outer tube through the wall of the door is set by means of a threaded inner sleeve, a threaded tube and a "C" shaped spring without any binding agent, and that other fixing means for the both members of the conventional door viewer of binding by the both flanges of the inner and outer tubes provides the male screw on the outer surface of the inner tube and the female screw on the inner surface of the outer tube, which the both flanges are exposed from the surface of the door, and the both tubes are screwed on the above stated screws.
U.S. Pat. No. 4,082,434 to Hayashi et al discloses a wide-angle optical system for door viewer which includes an inner sleeve illustrated in FIG. 1 of that patent wherein the opetical system of the two objective lenses and one eyepiece is assorted with each inner and outer tube and the inner sleeve. It is generally recognized that the inner sleeve or the lens tube 118 operates only as a stopper of the second objective lens from an embodiment illustrated in FIG. 7, since a convex lens 113 is appropriately positioned in the inner sleeve 118 or the like to coincise the both focal points F.sub.1 and F.sub.2.
A patent to Yamaguchi, U.S. Pat. No. 4,116,529 discloses a wide-angle spyglass comprising three lenses, a threaded inner sleeve and a threaded cylindrical member and a C-shaped spring for a stopper of an eyepiece. The threaded inner sleeve operates concurrently as the lenses stopper and an inner tube to fix thereof in an outer sleeve, since an objective is firstly fitted in the barrel member before the wide-angle lens and its fixture member are mounted to the barrel member.
A Japanese Utility Model Publication No. 22057/1971 of application to Yamaguchi discloses a wide angle door scope which includes an embodiment illustrated in FIG. 2 of that Utility Model Application wherein four lenses are assorted in the inner sleeve, and the third concave lens has a front concave surface and a rear flat surface, also an eyepiece is resiliently fixed on the inner peripheral surface of the inner sleeve. It is generally recognized that the inner sleeve operated the lenses stopper and a fixing member thereof in an outer sleeve.